Synthesis of Nitrogen-Conjugated 2,4,6-Tris(pyrazinyl)-1,3,5-triazine Molecules and Electrochemical Lithium Storage Mechanism

Abstract

Organic anode materials for lithium-ion battery have attracted widespread attention due to their diversity in organic linker functional species and the ability to tune their molecular levels. However, the rational design of advanced organic anodes with high reversible capacity and intentional organic molecular design requires a deep understanding of their mechanism for use in small-molecule organic rechargeable batteries. Herein, an optimized small-molecule-based organic anode material containing highly efficient active sites was developed for use in an organic lithium-ion battery. A small-molecule organic compound, 2,4,6-tris(pyrazinyl)-1,3,5-triazine (TPT), was formed by the trimerization of the 2-cyanopyrazine monomer. This molecule was rationally designed and evaluated as a lithium-ion battery organic anode material. TPT has a relatively small structure, but a superior reversible specific capacity was still achieved. Excitingly, TPT2 (liquid-phase synthetic) released a reversible capacity of 622 mAh g–1 at 100 mA g–1. Moreover, impressive long-term cycling performance was obtained, with a storage capacity of 541 mAh g–1 at 800 mA g–1 after 500 cycles. This demonstrated the durable cyclic stability of TPT2, which also achieved excellent rate performance at different current densities from 100 mA g–1 to 1.6 A g–1. The lithium storage mechanism of TPT was studied by theoretical calculations and ex situ Fourier transform infrared spectroscopy (FTIR) combined with X-ray photoelectron spectroscopy (XPS) characterization, which demonstrated that multiple active sites consisting of −C–N and −C═N groups were responsible for its superior lithium storage performance. This study provides a new understanding of the energy storage mechanism in small-molecule organic-based anode electrodes.